Nitrogen and phosphorus adsorption in aqueous solutions by humic acids from weathered coal: isotherm, kinetics and thermodynamic analysis

Inhibitory effects and mechanisms of insoluble humic acids on internal phosphorus release from the sediments

Release of phosphorus (P) from the sediments plays a critical role in the eutrophication of aquatic environments. Humic acids (HA), as the main form of carbon storage in the sediments, has essential impacts on the biogeochemical cycle of phosphorus in aquatic systems. Nevertheless, previous studies mainly concentrated on the competitive adsorption of HA solution and P on metal oxides and soils, with little attention paid to the effects of insoluble humic acids (IHA) on P sorption by and release from the sediments. Herein, an investigation on the rivers and lakes in Sichuan Province, China, found that there was a significantly positive correlation between the maximum P adsorption capacity (Qmax) of sediments and IHA contents (p < 0.01), but a significantly negative correlation between the zero equilibrium P concentration (EPC0) and IHA concentrations (p < 0.01). This indicated that IHA might have an inhibitory effect on the release of P from the sediments, which was verified by batch adsorption experiments and static incubation experiments. Adsorption experiments indicated that IHA can promote P adsorption by sediments. With the increase of IHA addition (from 0 to 20 mg/g) in the sediments, Qmax of sediments increased (from 0.516 to 0.911 mg/g), while EPC0 decreased greatly (from 0.264 to 0.005 mg/L). Increases in Fe (Ⅲ) bound-P, Al bound-P and humic bound-P caused by IHA were responsible for this promoting effect. Incubation experiments illustrated that IHA addition can efficiently inhibit P release from the sediments. After 32 days incubation, P concentration in the overlying water of control group (without IHA addition) was 0.651 mg/L, which was 13.29-40.69 times higher than those (0.016-0.049 mg/L) in the test groups (with 5 %-20 % IHA addition). The analysis of P species in sediments showed that transformation from loosely adsorbed-P and Fe (Ⅲ) bound-P to Al bound-P and humic bound-P was responsible for this inhibition of P release by IHA. This study demonstrated that IHA, differing from readily degradable or dissolved organic matter, have great inhibitory effects on internal P release, which provided a novel insight into the association between carbon burial and internal P release and even the management of water eutrophication.

Monitoring of Nitrogen Transport Data in Pear Leaves Based on Infrared Spectroscopy

In order to better monitor the data of nitrogen transport in pear leaves, a method based on infrared spectroscopy was proposed. The near-infrared reflection spectrum imaging technology is used to collect the leaf scale spectral image of the target crop. Computer image analysis software is used to process the spectral digital image and extract the spectral data. After statistical analysis, the data are selected as variables. Combined with the chemical analysis test results, the crop nutrition detection model is established, and the conclusion is drawn. The experimental results show that the band gray data involved in the model are scaled and reorganized according to the coefficient proportion by using ENVI through the band calculation command. The final gray image, the original image, and the gray image in the process default to the three-channel analog image of the band (the wavelengths of the bands are 1446, 1373, and 1304 nm, respectively); 944 nm gray image; 1043 nm gray scale image; 1662 nm gray image; (0.102R944 +0.103R1 043 +0.206R1662)/(0.102 + 0.103 + 0.206) grayscale image with signal scaling according to the scale of model coefficient. It is proved that infrared spectroscopy can effectively monitor the data of nitrogen transport in pear leaves.

Recovery of NH4 +-N and PO4 3--P from urine using sludge-derived biochar as a fertilizer: performance and mechanism

Sludge-derived biochar (BS) was prepared by pyrolyzing municipal sludge at different temperatures and was used to recover NH4 +-N and PO4 3--P from urine. The effects of dosage, adsorption time, and urine concentration on the adsorption of NH4 +-N and PO4 3--P were investigated, and the adsorbed BS was used as a fertilizer to study its effect on the growth of pakchoi cabbage. The Elovich model was more consistent with the adsorption processes of NH4 +-N and PO4 3--P. Both the NH4 +-N and PO4 3--P adsorption isotherm model agreed with the Redlich-Peterson model. The Langmuir model showed that the largest adsorption capacity of BS600 for NH4 +-N and PO4 3--P could reach 114.64 mg g-1 and 31.05 mg g-1, respectively. The NH4 +-N adsorption mechanism of BS may have complexation with O-containing functional groups and precipitation reactions, while the removal mechanism of PO4 3--P was co-precipitation. The pot experiment demonstrated that adsorbed BS600 can better promote the growth of pakchoi cabbage with the same amount of addition. With the addition of 5% adsorbed BS600, the weight of cabbage was 64.49 g heavier than without the addition of BS600. This research provided theoretical support for the recovery of NH4 +-N and PO4 3--P from urine as a fertilizer.

Characterization of humic acids from original coal and its oxidization production

Five coal samples obtained from Chinese coal-producing areas were oxidized by hydrogen peroxide (H₂O₂), and humic acids (HAs) were derived from original coal and its oxidizition samples. HAs were characterized by physical and chemical methods, between which was also comparison. Yield, ash, aromaticity, molecular weight and functional group of HAs showed variance between original coals. While, yield, molecular weight, and the quantity of oxygen-containing groups of HAs increased more from coals oxidized with H₂O₂. However, the increase of oxygen-containing functional groups depended on original coals. For Yimin lignite, the oxidation of H₂O₂ could obviously improve the carboxyl group content of HAs, thus promoting the adsorption of nitrogen. This study demonstrated that oxidation of coal by using H₂O₂ was one pretreatment way to obtain and modify HAs which could be used as prerequisite and functional material in agricultural field.